This invention relates to a catalytic system for polymerizing olefins, particularly propylene and comonomers. The present invention involves a novel support for catalysts containing titanium, the supported catalysts comprising electron-donor compound and titanium halide, a cocatalyst containing an organometallic compound, a process for producing the supported catalyst, and use of the catalytic system to polymerize olefins by the coordinate complex (Ziegler-Natta) method.
The coordinate complex approach to polymerizing olefins has been known for 30 years, and thousands of catalytic systems involving that approach have been disclosed. The present invention is a novel and useful catalyst for polymerizing olefins with high activity and stereospecific control.
Activity is normally measured by the grams of polyolefin produced per gram of catalyst containing titanium or other transition metal. High activity leads to a low amount of metallic ash and corrosive halide left in the polymer. If the activity is high enough, e.g., 10,000, then the de-ashing step in processing the final polyolefin can be omitted--an important improvement.
For olefins such as propylene which can form isotactic structures, high isotacticity (stereospecificity) (up to about 97 percent) gives better physical properties to the polymer. Isotactic polypropylene is more ordered, less soluble in halocarbons or hydrocarbons, and useful for its higher strength than the more soluble atactic form. Isotactic indices (defined below) of 93 or higher are favored for commercial polypropylene.
U.S. Pat. No. 3,238,146 granted to Hewett and Shokal discloses a polymerization catalyst for olefins comprising crystals of salts of a metal with an atomic weight between 24 and 209 vacuum-plated with a molecularly thin layer of salts of dissimilar metals. Preferred substrate salts are rhombohedral such as cobaltous, magnesium, manganese, and cadmium dichlorides. Preferred coatings, 10 to 100 molecules thick, are halides of metals with atomic volumes between 5 and 15 such as titanium, vanadium, and zirconium.
U.S. Pat. No. 3,008,945 discloses a catalyst system for polymerizing isoprene with stereochemical control comprising an aluminum alkyl, titanium tetrachloride, and ferric chloride.
U.S. Pat. No. 2,954,367 discloses a slurry for polymerizing vinyl compounds comprising the reaction product of a halogen-free organometallic compound with compounds of metals from Groups IVB, VB, VIB or VIII of the periodic table of the elements.
U.S. Pat. No. 4,048,418 discloses a catalyst system for polymerizing dienes comprising an organometallic reducing agent from Groups I and III of the periodic table, a ligand containing nitrogen and a compound containing iron such as ferric salts of organic acids, FeCl.sub.3, or FeCl.sub.2.
All four of the disclosures cited above are incorporated by reference into this application.